1. Field of the Invention
The present invention relates to a projection optical system that projects an image, which is displayed by a reflective light valve, onto a screen in a enlarged manner and the projection-type display apparatus having the same, in particular, to a projection optical system, which has a small size with good mobility and has a light source with a relatively small luminance, and a projection-type display apparatus having the same.
2. Description of the Related Art
Recently, in the projectors, there has been a demand for highly portable mobile projectors.
Among such mobile projectors, there is a convenient projector which is able to project an image onto a desirable location (for example, a wall or a ceiling) while being held in one hand as if using a flashlight or a penlight.
However, there are known reflective light valves that can be mounted on such a projector, such as a reflective liquid crystal display device (a LCOS) and a DMD (a Digital Micro Device). The reflective light valves have an advantage in that it is possible to increase the aperture ratio thereof as compared with that of the transmissive light valve, increase the efficiency of light conversion, and promote compactness of the projector.
On the other hand, generally, a known arrangement of the projection optical system is as follows: a PBS (a polarization beam splitter prism) as a polarized light separation section is disposed between the projection lens and the reflective light valve, the illumination light originating from the light source section is made to be incident to the reflective light valve through the PBS, the optical path of the light modulated by the reflective light valve is separated from the optical path of the illumination light by the PBS, and the modulated light is projected toward the screen by using the projection lens.
However, in such a projection optical system, when the PBS has the incident angle characteristics and the angle of light incident on the polarized light separation surface has a range, the disadvantages such as the luminance unevenness and the color unevenness may arise. For this reason, it is necessary to make the illumination light incident to the PBS in a telecentric state, and thus it is also necessary to adopt a configuration in which the projection lens is formed to be telecentric on the reduction side and then the PBS and the reflective light valve are disposed.
FIG. 16 shows an example of the projection display apparatus equipped with the projection optical system used in the related art. That is, an illumination optical system 120 includes: three-color. LED light sources 111a to 111c; dichroic mirrors 112a and 112b; fly-eye integrators 113a and 113b that serve as sections that uniformizes the light amount; a comb-like filter 114 that shapes the illumination light into the several linear polarized rays (P-polarized light or S-polarized light); and a pair of field lenses (condenser lenses) 115a and 115b. The illumination light emitted from the illumination optical system 120 is incident to a PBS 101 of a projection optical system 110. The illumination light incident to the PBS 101 is shaped in the predetermined linear polarization direction, and is reflected toward a reflective liquid crystal display device 103 on the polarized light separation surface. Then, in the reflective liquid crystal display device 103, the illumination light is modulated on the basis of a predetermined image signal, and is converted into the linearly polarized light with the opposite phase. Thereafter, the modulated light reflected and emitted from the reflective liquid crystal display device 103 is converted into the linearly polarized light with the opposite phase, is therefore transmitted through the polarized light separation surface of the PBS 101, and is projected onto a screen in an enlarged manner by the projection lens 102.
However, in the example of the related art shown in FIG. 16, as described above, it is necessary to secure the back space into which the PBS can be inserted while the projection lens 102 is formed to be telecentric on the reduction side. Thus, particularly the diameters of the lenses closer to the reduction side in the projection lens increase, and as a result, a problem arises in that it is difficult to achieve compactness in the projection optical system and the projection-type display apparatus. Further, in the example of related art shown in FIG. 16, it is necessary to consider the incident angle characteristics of the polarized light separation surface when the rays emitted from the illumination optical system 120 are incident to the PBS 101. For this reason, the condenser lenses 115a and 115b are necessary in order to make the rays, which are emitted from the illumination optical system 120, telecentric. This causes problems such as an increase in cost and size of the projection optical system.
The projection optical systems disclosed in JP-A-4-326315 and JP-A-5-203872 which are able to achieve compactness of the optical system in consideration of the arrangement of the optical elements in order to cope with the problems mentioned above have been known.